The invention relates to the production of a metal can, comprising a cylindrical body, a base and a lid, of the type in which the base has a cylindrical, or virtually cylindrical, recess which projects into the inside of the can. The invention also relates to metal cans of this nature.
Where the following text refers to a can, what is meant, in the first instance, is a can which is suitable for packaging foodstuffs, such as drinks or food.
However, the invention is also deemed to relate to the production of a can which is intended to hold different contents.
A new development in the use of cans consists in the fact that a need has arisen for cans which are provided with means for heating or cooling them. If such cans are taken to places where there are no facilities for heating or cooling the contents of the can, such added features still allow the contents of the can to be brought to the desired temperature.
Numerous proposals have been made for designs in which a heating or cooling element is situated in the can, in which case the heating or cooling element can be activated by external means.
For various reasons, there is a need for an embodiment of a can of this nature in which the heating or cooling element is situated outside the actual contents of the can, so that there is no risk of the contents of the can coming into contact with chemicals. By, way of example, it is proposed in patent WO-9629255 to design the base with a cylindrical recess which projects into the inside of the can. If this recess is large enough, an element for cooling or heating the contents of the can can be placed therein.
Different therefrom patent U.S. Pat. No. 3,494,143 describes a can in which a cooling or heating cartridge is built-in in the can. The cartridge is affixed by folded seams to the interior side of the separate base of the can. This results in a complicated construction with the further disadvantage that any leakage from the cartridge through the folded seem mixes up with the contents of the can. The present invention relates to a novel method for the production of a metal can provided with such a recess in the base, and to a can of this nature. The object of the invention is to provide a simple design which follows on from known production techniques for, for example, metal drinks cans and in which the weight of the can is very low. The present invention also has the object to obviate disadvantages of known constructions.
The invention therefore consists in the fact that, in the method mentioned in the preamble:
a) a combination of a body and a base is produced, by deep-drawing and wall stretching, from metallic and/or plastic-coated metal sheet which is suitable for cans;
b) an insert piece, which is tubular in shape so as to correspond to the cylindrical recess and is closed on one side, is produced from corresponding metal sheet by deep-drawing or spinning, followed by wall stretching;
c) a hole which is narrower than the open side of the insert piece is made in the base of the body-base combination;
d) the edge of the hole is flanged until it acquires a bearing surface which is able to fit together with the edge of the open side of the insert piece;
the edge of the hole and the edge of the open side of the insert piece are joined together.
It will be clear that after the can has been filled, the lid is attached to that side of the body which is remote from the base.
Where a cylindrical recess is referred to, this is also understood to encompass recess shapes which differ only slightly from a true cylinder, for example recesses which taper slightly.
It should be noted that the above-mentioned step a) corresponds to the production of a body-base combination for a so-called two-part can. This is therefore entirely compatible with widely used techniques for producing cans in vary large quantities. In fact, the above-mentioned step b) also employs the same technique on a component which has only a slightly different shape. As a result, all the experience in producing cans which has been gained can be employed so as to obtain a weight which is as low as possible. After production, cans are often also provided with a protective coating on the inside. When using the novel process, it is preferable to provide the outer surface of the insert piece with the same protective coating as that which is customarily applied to the inside of the can. If suitable equipment is available, it is obviously conceivable to apply the protective coating after the edge of the hole and the edge of the insert piece have been joined together. However, it will often be preferable to provide the inside of the can with the protective coating before a hole is made in the base and to provide the outside of the insert piece with the coating before the edge of the hole and the edge of the insert piece are joined together.
A suitable method according to the invention for joining together the insert piece and the edge of the hole has proven to be one in which firstly the edge of the hole is flanged outwards, and then the edges of the open side of the insert piece and of the hole are both beaded and then folded together. It should be noted that joining edges by means of beading and folding is a method which is known and has been tried and tested, and therefore does not need to be described in more detail. It is, however, preferable first of all to arrange a sealing compound, which is known per se, in the beaded edge of the insert piece, before the bead edges are folded together. This sealing compound ensures that the contents of the can cannot be contaminated from outside via the folded-together bead edge.
The most simple way of beading the edge of the hole and folding together the edge of the hole and the edge of the insert piece is if the flanged edge of the hole extends beyond, in the axial direction, that point of the base which projects furthest. However, it is undesirable for the folded-together edge ultimately to project so far that it will then have to serve as the support edge of the filled can, since in many cases this is considered undesirable. Therefore, it is preferred, after the folding operation has been carried out, to press the folded-together edge towards the can as far as beyond that point of the base which projects furthest in the axial direction.
According to another method for joining the edge of the hole and the edge of the insert piece, the edge of the hole is firstly flanged towards the inside of the can, after which the flanged edge of the hole and/or the edge of the open side of the insert piece are provided with adhesive and are then joined together.
According to the invention, by pushing the edge of the open side of the insert piece around the flanged edge of the hole until it bears against the base of the can, the insert piece and can body can be positioned very accurately and uniformly with respect to one another.
The invention relates not only to the process described but also to a metal can comprising a cylindrical body, a base and a lid, of the type in which the base has a cylindrical recess which projects into the inside of the can. According to the invention, this known can is designed in such a manner that the body and that part of the base which lies outside the recess comprise a single piece which is delimited by the edge of a hole in the base, which edge is flanged in the axial direction, and in that a tubular insert piece which forms the recess and is closed on one side has an edge which fits against the flanged edge of the hole and is joined thereto. In this novel can, the outer surface of the insert piece is preferably provided with the same protective coating which is customarily applied to the inside of the can. As has already been described above with reference to the description of the production of the novel can, the edge of the hole can be flanged towards the contents of the can, the edges of the open side of the insert piece and of the hole both being beaded and then folded together. In this case, a sealing compound may be present in the fold seam.
In a preferred embodiment of the novel can, the fold seam of the folded-together edges is located, in the direction of the can, beyond that point of the base which projects furthest in the axial direction.
In another embodiment of the novel can, the edge of the hole is flanged towards the inside of the can, in which case the flanged edge of the hole and/or the edge of the open side of the insert piece are joined together by means of adhesive. In this case, the open side of the insert piece is preferably pushed around the flanged edge of the hole until it bears against the base of the can.